1. Field of the Invention
This invention relates to an optical wavelength converting apparatus for converting a fundamental wave into its second harmonic, or the like. This invention particularly relates to an optical wavelength converting apparatus, wherein a plurality of wavelength-converted waves having different wavelengths are obtained.
2. Description of the Prior Art
Various attempts have heretofore been made to convert the fundamental wave of a laser beam into its second harmonic, or the like, e.g. to shorten the wavelength of a laser beam, by using a nonlinear optical material. As optical wavelength converting devices for carrying out such wavelength conversion, there have heretofore been known a bulk crystal type of optical wavelength converting device, an optical waveguide type of optical wavelength converting device, and the like.
In cases where the wavelength of a laser beam is shortened in the manner described above, such that a plurality of wavelength-converted waves having different wavelengths may be obtained in a state combined with one another, a fundamental wave produced by a single light source or fundamental waves produced by a plurality of light sources impinge upon one of a plurality of independent optical wavelength converting devices and then impinge upon another optical wavelength converting device. Specifically, for example, when a single fundamental impinges upon one of two independent optical wavelength converting devices and then upon the other optical wavelength converting device, the second harmonic of the fundamental wave can be generated in the first optical wavelength converting device, and the third harmonic of the fundamental wave can be generated in the second optical wavelength converting device. Also, when first and second fundamental waves, which are in the state combined with each other, impinge upon one of two independent optical wavelength converting devices and then impinge upon the other optical wavelength converting device, the second harmonic of the first fundamental wave can be generated in the first optical wavelength converting device, and the second harmonic of the second fundamental wave can be generated in the second optical wavelength converting device.
However, in cases where a fundamental wave or fundamental waves impinge upon one of a plurality of independent optical wavelength converting devices and then impinge upon another optical wavelength converting device in the manner described above, the fundamental wave or fundamental waves are reflected many times by end faces of the devices. Also, often when a wavelength-converted wave whose wavelength has been converted by a certain optical wavelength converting device impinges upon a different optical wavelength converting device, the wavelength-converted wave is reflected by an end face of the different optical wavelength converting device. Therefore, it is not always possible to obtain a wavelength-converted wave having a high intensity.